Smart meters are starting to be used in Europe and in the United States, and demonstration experiments of smart meters are starting to be held in Japan. A smart meter is an electricity meter having a communication function. A smart meter may report the amount of electricity usage to an electric power provider via a network. If smart meters are installed in households, there is no need for personnel to read meters.    Patent document 1: Japanese Laid-Open Patent Publication No. 2003-242063
A smart meter having a wireless communication function is also being proposed. It would be convenient to distribute firmware by wireless communication with the use of such a smart meter. For example, with the use of the technology described in patent document 1, firmware of smart meters may be distributed.
However, in the technology described in patent document 1, a table instructing the order of distribution is to be set in the servers in advance. Thus, in a network environment including nodes such as smart meters that may be installed and removed any time, it is inefficient to set such a table.
By performing multi-hop broadcasting, firmware may be distributed to each smart meter. In broadcasting, the distribution destination is not limited to a particular node, and according to multi-hop, firmware may be distributed to a wide range of nodes.
However, when data having a relatively large size such as firmware is multi-hop broadcast by a narrow radio-frequency range such as IEEE 802.15.4, the network may be temporarily disturbed. Generally, large-sized data is transferred by being divided in plural blocks. When each block is broadcast by multi-hop, and network disturbance occurs in a particular block, the distribution of the next block is delayed until the disturbance ceases. If such waiting periods accumulate, it may take a long time to transfer all of the blocks.